1. Field of the Invention
The present invention relates to vibration control and, in particular, an apparatus and method for controlling vibration of a movable platform, such as an elevator cab.
2. Description of the Related Art
Vibration control isolation and mounting systems are well known in the art, including passive, fluid, and active systems. Passive systems utilize passive isolating devices such as mountings and spring and shock absorber arrangements to isolate a suspended member from shock and vibration inputs.
U.S. Pat. Nos. 4,811,919, 5,197,692, and 5,127,607 disclose fluid mountings and fluid systems for improving vibration isolation. In particular, the fluid mountings utilize tuned fluid inertial forces to provide a tuned resonant frequency and non-linear mount characteristics. Although these fluid mountings and systems provide improved isolation as compared to passive systems, they still provide inadequate isolation for some applications because the fluid tunability has only a limited tuning range and the stiffness cannot be zero at the tuned frequency.
For optimum isolation, active forces need to be developed which are added to, or subtracted from, the input disturbances in the proper phase relationship to minimize transmitted vibration regardless of the frequency of the disturbance. U.S. Pat. No. 5,174,552 is an example of such an active system. Although this system provides superior isolation, it utilizes fluid as the active actuator medium, which may not be desired in some applications.
U.S. Pat. No. 4,624,435 describes a dry system including a resilient vibration isolator and an electro-magnetically controllable vibration damping arrangement. U.S. Pat. No. 5,219,037 also includes an electromagnetic actuator including a first elastomer section and a second elastomer section. The first section is stiff radially and soft axially for protecting the actuator from side loads. The second elastomer section accommodates shear motions in the mounting. In Smith, an elastomer is shown placed in series-spring relationship with the actuator; however, no mention is made of the characteristics of the elastomer. Furthermore, these voice coil systems are typically used for higher amplitude and relatively low force applications. This is because voice coil actuators do not function adequately at low amplitudes.
An object of the present invention is to isolate a movable platform from vibration forces transmitted to the movable platform.
According to an aspect of the invention, the movable platform is the floor of an elevator cab. One or more supports attach the elevator cab to a carriage, which is connected to a drive mechanism for transporting the elevator cab. Each support includes a piezoelectric element and a passive vibration attenuator so as to actively isolate the elevator cab from drive-mechanism generated vibration transmitted through the carriage. The piezoelectric element is preferably connected in series with the passive vibration attenuator so as to substantially cancel out any vibration transmitted through the passive vibration attenuator.
In one embodiment, there is provided an apparatus for actively controlling transmission of vibration energy to a movable platform mounted to a carriage for transporting the movable platform. The apparatus includes a passive vibration attenuator for passively absorbing vibration energy transmitted through the carriage. Also included is a vibration sensor comprised of a first piezoelectric material and connected in series with the passive vibration attenuator. The vibration sensor is configured to generate an electrical signal in response to deformation of the vibration sensor caused by vibration energy transmitted through the passive vibration attenuator. An inverter inverts the electrical signal from the vibration sensor and outputs an inverted electrical signal that is equal in magnitude and opposite in polarity to the electrical signal from the vibration sensor. A vibration generator, responsive to the inverted electrical signal and connected in series with the vibration sensor, is comprised of a second piezoelectric material for transmitting a vibration force to substantially cancel the vibration energy transmitted through the passive vibration attenuator.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.